The sluggish oxidants, [FeIV(O)(TMC)(CH3CN)] 2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) and [FeIV(O)(d12-TMCN)(OTf)] + (3d; d12-TMCN = 1,4,7,11-tetra-d3-methyl-1,4,7,11-tetraazacyclotetradecane), are transformed into a highly reactive oxidant, [FeIV(O)(TMCO)(OTf)] + (1; TMCO = 4,8,12-trimethyl-1-oxa-4,8,12-triazacyclotetradecane), upon replacement of a -NMe donor in the TMC and TMCN ligands by an O-atom. A rate enhancement of 5 – 6 orders of magnitude in both H-atom and O-atom transfer reactions is observed upon oxygen incorporation into the macrocyclic ligand and can be explained based upon the higher electrophilicity of the iron center and the higher availability of the more reactive S = 2 state in 1. This rationalizes nature’s preference for using O-rich ligand environments for the hydroxylation of strong C-H bonds in enzymatic reactions.
The paper was published today in Angew. Chem. Int. Ed. (DOI: 10.1002/anie.201707872):
I. Monte Pérez, X. Engelmann, Y-M. Lee, M. Yoo, K. Elumalai, E.R. Farquhar, E. Bill, J. England, W. Nam, M. Swart and K. Ray
“A Highly Reactive Oxoiron(IV) Complex Supported by a Bioinspired N3O Macrocylic Ligand”
Angew. Chem. Int. Ed. 2017, ASAP [abstract]